Method for recovering hydrogen from biomass pyrolysis gas

ABSTRACT

A method for recovering hydrogen which is capable of efficiently recovering high concentration hydrogen gas by adsorbing and removing hydrocarbon gas such as carbon dioxide from biomass pyrolysis gas under a relatively low pressure, and also capable of storing the recovered high concentration hydrogen gas, preferably, in a cartridge type container that can be used as is as a hydrogen storing container for an apparatus equipped with a fuel cell. The method includes a first purifying stare of purifying biomass pyrolysis gas and a second purifying stage of purifying the obtained purified gas under a pressure equal to or less than the pressure in the first purifying stage to recover gas that contains hydrogen, and further includes a hydrogen storing stage of feeding the gas containing hydrogen recovered in the second purifying stage into the container filled with a hydrogen storage alloy and storing high purity hydrogen.

TECHNICAL FIELD

The present invention relates to a method for recovering hydrogen frombiomass pyrolysis gas, and more specifically relates to a method forpurifying and recovering hydrogen from pyrolysis gas obtained byheat-treating biomass, as well as simultaneously storing the purifiedhydrogen in a container which can be used as it is as a hydrogen storagecontainer in an instrument equipped with a fuel cell utilizing hydrogenas fuel, for example. In the present invention, the term “pyrolysis gas”includes not only the above-described pyrolysis gas obtained byheat-treating biomass but also gas obtained by further steam-reformingthe pyrolysis gas.

BACKGROUND ART

In recent years, products utilizing a fuel cell are becoming widespread,and an example thereof is a household apparatus for supplyingthermoelectricity using solid polymer-type fuel cells. Another examplethereof is a fuel-cell vehicle. Accordingly, research and development oftechniques for producing, storing and transporting hydrogen have beenactivated.

On the other hand, mobile terminal devices such as mobile phones andsmart phones are also becoming widespread. As a power source thereof, alithium ion battery is utilized. In order to prolong the battery life ofthe mobile terminals, the performance of the lithium ion battery isbeing improved. Although improvement of the performance of the lithiumion battery is an exemplary measure to extend the use time of the mobileterminal devices, as another measure, an instrument for power supply ofthe mobile terminals is to be developed and commercialized in which asmall fuel cell and a hydrogen storage container (e.g., cartridge) areintegrated. As the hydrogen storage container, containers made of ahydrogen occlusion alloy, a carbon-based porous material, an inorganiccomplex-based materials, an organic chemical hydride, and the like havebeen studied. Thus, in recent years, hydrogen has attracted attention invarious industries, and it is expected that the demand will be greatlyincreased.

Conventionally known methods for producing hydrogen include, e.g.; amethod for separating and recovering hydrogen from coke oven gas; amethod for separating and recovering hydrogen from blast furnace gas; amethod for separating and recovering hydrogen from naphtha-reformed gasgenerated in a petroleum refining complex; a method for separating andrecovering hydrogen generated from a salt electric field; a method forproducing hydrogen by electrolysis of water; and the like. Recently,techniques such as a method for separating and recovering hydrogen frommethanol-reformed gas or a method for separating and recovering hydrogenfrom natural gas and methane-reformed gas have been established andpracticalized.

As recent new approaches, a method for producing hydrogen by means ofalgae using hydrogen fermenting bacteria; a method referred to as “Powerto Gas” for producing hydrogen by means of water electrolysis usingelectric power from solar power generation, wind power generation andsmall hydroelectric generation; a method for separating and recoveringhydrogen obtained by pyrolysis gas of biomass, and the like have beenproposed, and some of them have been demonstrated.

As techniques for storing and transporting hydrogen: a method in whichhydrogen is charged into a high-pressure gas cylinder, and stored andtransported in that state; a method in which an organic solvent such asnaphthalene or toluene is hydrogenated (e.g., naphthalene is transportedin a form of tetralin, or toluene is transported in a form ofmethylcyclohexane), and then separated into naphthalene or toluene andhydrogen at each demander so as to utilize hydrogen, and the like havebeen proposed.

With respect to the method for producing hydrogen as described above, ina method other than water electrolysis, the obtained hydrogen should beseparated and recovered from other gas such as carbon dioxide, carbonmonoxide, a hydrocarbon gas including methane, or toluene, naphthaleneand the like. In addition, a variety of such methods for separating andrecovering hydrogen gas from other gas have been proposed.

As a gas separation method for blast furnace gas containing carbondioxide, nitrogen, hydrogen and carbon monoxide, a pressure swingadsorption-type gas separation method carried out by using a pluralityof an adsorption column filled with an adsorbent having a carbon dioxideadsorption capacity higher than each of hydrogen, carbon monoxide andnitrogen absorption capacity and a hydrogen adsorption capacity lowerthan each of carbon monoxide and nitrogen adsorption capacities, e.g.,an active carbon, or for example, a separation method of a blast furnacegas in which mainly carbon dioxide in blast furnace gas is adsorbed intothe above-described adsorbent by PSA (Pressure Swing Adsorption) in ahigh pressure state, and mainly hydrogen is recovered as an unadsorbedgas, has been disclosed (Patent Document 1). In Examples, a separationmethod using a single-stage PSA with three adsorption columns and anapparatus therefor are used, and thereby carbon dioxide and hydrogen areseparated from the blast furnace gas. This method was single-stage styleand was carried out at a relatively low pressure of 300 kPa, buthydrogen concentration of the recovered gas was not so high as 60 to70%.

A hydrogen producing apparatus has been disclosed comprising: areforming reaction tube housing a reforming catalyst promoting areforming reaction for producing hydrogen from hydrocarbons and water,and a carbon dioxide absorbent; a feed unit for feeding a source gas tothe reforming reaction tube; a purification unit for separating thereformed gas output from the reforming reaction tube into a product gaswith increased concentration of hydrogen and an off-gas with increasedconcentration of non-hydrogen components; a return unit for returningthe off-gas from the purification unit to the feed unit; and a carbondioxide-withdrawing unit for withdrawing carbon dioxide-rich gas fromthe reforming reaction tube by depressurizing the reforming reactiontube (Patent Document 2). In this apparatus, carbon dioxide produced bythe reforming reaction is adsorbed in the reforming reaction tube,thereby a concentration of carbon dioxide is decreased to increase theconcentration of hydrogen in the reformed gas. Thus, there have beennecessities that the reforming reaction tube is filled with the carbondioxide-absorbing material, and the reforming reaction tube is heated tohigh temperature in order to regenerate the carbon dioxide-absorbingmaterial.

For a hydrogen-producing apparatus in which a hydrogen-containing gas isproduced from a hydrocarbon as a raw material by a reformer, theproduced hydrogen-containing gas is separated by a hydrogen purificationapparatus (PSA) into hydrogen and a concentrated impurity gas containingconcentrated gas components other than hydrogen, and the separatedhydrogen is recovered as high-purity hydrogen, a method for reducing anamount of carbon dioxide emission has been disclosed comprising: burningcombustible components in the concentrated impurity gas by a combustionapparatus; and removing carbon dioxide in the combustion gas by adecarbonator (Patent Document 3). Herein, the decarbonator is filledwith a carbon dioxide-adsorbing material, e.g., a calcium oxideadsorbent, and carbon dioxide can be adsorbed and removed, but theadsorbed carbon dioxide cannot be reused. In addition, there has been aproblem that although the used adsorbent can be reused as a cementsolidifying material, it cannot be reused as an adsorbent.

A hydrogen-producing method accompanied with recovery of a liquefied CO₂has been disclosed, comprising: steam-reforming a natural gas fed in aform of liquefied natural gas into a hydrogen-rich reformed gas;separating and purifying hydrogen from this reformed gas; and usingoff-gas containing combustibles separated in the purification process ofhydrogen as a main fuel for combustion and heating in the reformingprocess, in which method: pure oxygen or highly concentrated oxygenobtained by cryogenic separation using liquefaction cold of liquefiednatural gas is introduced as an oxidizer for burning the off-gas in thereforming process; the CO₂ gas in the combustion exhaust gas generatedin this combustion is concentrated to easily separate and recover theCO₂ gas in a liquid state from the combustion exhaust gas; separated andpurified hydrogen is pre-cooled by the liquefied natural gas and thencooled and liquefied by liquid nitrogen obtained in the cryogenic airseparation; and the liquefied natural gas after used for pre-cooling ofhydrogen is utilized to liquefy the CO₂ gas and fed to the reformingprocess of hydrogen (Patent Document 4). There has been a problem thatthis method utilizes cold generated in vaporizing the liquefied naturalgas, and thus the place for using the method is limited.

A hydrogen-producing and carbon dioxide-recovering method for producinghydrogen from carbon-containing fuel and recovering carbon dioxide hasbeen disclosed, comprising: a hydrogen-containing gas producing process,in which the carbon-containing fuel is reformed to obtain thehydrogen-containing gas containing hydrogen and carbon dioxide; a PSAprocess, in which the hydrogen-containing gas is separated into firsthydrogen-rich gas containing enriched hydrogen and PSA off-gascontaining enriched components other than hydrogen by means of apressure swing adsorption apparatus; a carbon dioxide-membraneseparation process, in which the PSA off-gas is separated into carbondioxide-rich gas containing enriched carbon dioxide and carbon dioxideseparation membrane off-gas containing enriched components other thancarbon dioxide by means of a carbon dioxide separation membrane; and ahydrogen membrane separation process, in which the carbon dioxideseparation membrane off-gas is separated into second hydrogen-rich gascontaining enriched hydrogen and hydrogen separation membrane off-gascontaining enriched components other than hydrogen by means of ahydrogen separation membrane (Patent Document 5). In the method, aseparation process by a single-stage PSA and an apparatus therefor areused, and the off-gas discharged from the PSA is further separated intothe hydrogen-rich gas and the gas containing the enriched componentsother than hydrogen by using the carbon dioxide separation membrane andsubsequently using the hydrogen separation membrane.

A method for purifying a hydrogen gas containing an impurity gas bymeans of a hydrogen occlusion alloy has been proposed (Patent Document6). This method comprises: supplying the hydrogen gas containingimpurities to the hydrogen occlusion alloy to let the alloy occlude thehydrogen gas; removing the impurities; and heating the hydrogenocclusion alloy to let the alloy release hydrogen. Therefore, the methodrequires not only pressure change but also a heating operation. Also, amethod has been proposed which comprises: a first removal step forremoving CO from a modified gas; a second removal step for removingunnecessary gases other than CO from the obtained CO-removed gas; atemporal storage step for storing the resulting high-purity hydrogen ina buffer tank; and a hydrogen occlusion and release step for recoveringhydrogen from an off gas from the second removal step, wherein thehigh-purity hydrogen and the hydrogen from the hydrogen occlusion andrelease step are utilized as a cleaning gas for recycling an adsorbentin the above-mentioned steps and a gas for pressurizing an adsorptioncolumn (Patent Document 7). The method attempts to decrease a loss ofproduct hydrogen and to recover high-purity hydrogen from the reforminggas with high recovery rate. However, since the method uses hydrogenoccluded in the hydrogen occlusion alloy for recycling the absorbent, arecovered amount of hydrogen is inevitably decreased. In addition, atemperature to release hydrogen from the hydrogen occlusion alloy is ashigh as 200° C.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP Pat. No. 5647388

Patent Document 2: JP Pat. No. 5134252

Patent Document 3: JP 2004-292240 A

Patent Document 4: JP Pat. No. 3670229

Patent Document 5: JP Pat. No. 5039408

Patent Document 6: JP Pat. No. 3897854

Patent Document 7: JP Pat. No. 5690165

Patent Document 8: WO 2015/011826

Patent Document 9: PCT/JP2015/080452

Patent Document 10: JP Pat. No. 4246456

Patent Document 11: JP Pat. No. 5463050

SUMMARY OF INVENTION Problem to be Solved

The present invention provides a hydrogen recovery method in whichcarbon dioxide, carbon monoxide and hydrocarbon gas such as methane canbe adsorbed and removed from pyrolysis gas obtained by heat-treatingbiomass at a relatively low pressure to efficiently recover highlyconcentrated hydrogen gas, and which can simultaneously store therecovered highly concentrated hydrogen gas in a predetermined container,preferably a cartridge-type container which can be used as it is as ahydrogen storage container in an instrument equipped with a fuel cellutilizing hydrogen as fuel.

Solution to Problem

The aforementioned prior art describes a method for separating andrecovering hydrogen and carbon dioxide from mixed gas containinghydrogen and carbon dioxide, carbon monoxide and hydrocarbon gas such asmethane, and the method uses, as a separation apparatus, a so-calledmulti-column type single-stage adsorption and separation-style PSAapparatus, in which a plurality of adsorption columns are used inparallel arrangement. Furthermore, in order to enhance separation orremoval of carbon dioxide, besides the PSA apparatus, an adsorbent or aseparation membrane is additionally used in combination. In themulti-column type single-stage adsorption and separation-style PSAapparatus, although hydrogen could be separated and recovered at arelatively low pressure, the hydrogen concentration in the recovered gaswas not to be sufficiently high. In addition, an excessively highpressure was not preferred from the viewpoint of not only increase ofoperation and apparatus costs but also safety of operation. Thus, it wasconceived to use the adsorbent or the separation membrane in combinationin order to increase the hydrogen concentration, but this was not to bepreferred because of its high cost.

In order to solve the above problems, the inventors have already filedmethod for recovering hydrogen from pyrolysis gas obtained byheat-treating biomass, comprising: a first purification step in whichcarbon dioxide is adsorbed and removed from the pyrolysis gas underincreased pressure to purify the pyrolysis gas; and a secondpurification step in which the purified gas obtained from the firstpurification step is further pressurized while keeping the pressure inthe first purification step, and further purified by adsorbing andremoving gas other than hydrogen from the purified gas under increasedpressure to recover hydrogen from the purified gas, and in this method,carbon dioxide adsorbed and removed in the first purification step isrecovered (Patent Document 8). According to this method, highlyconcentrated hydrogen can be recovered from the biomass pyrolysis gas ata relatively low pressure.

For the hydrogen recovery method using a so-called multi-column typedouble-stage adsorption and separation-style PSA apparatus as describedabove, the inventors found that even if the pressure in the secondpurification step was set to a pressure not higher than that in thefirst purification step, preferably even if the pressures in both of thefirst and second purification steps were set to low pressures of 0.15MPa to 0.6 MPa, carbon dioxide, carbon monoxide, a hydrocarbon gas suchas methane and the like could be sufficiently separated from the biomasspyrolysis gas to recover gas with highly concentrated hydrogen, and theinventors have already filed this finding (Patent Document 9). Accordingto this method, highly concentrated hydrogen can be recovered from thebiomass pyrolysis gas with a far lower pressure than that in the methodaccording to Patent Document 8 so that more efficient and economicaloperations can be achieved.

In order to further improve the methods according to Patent Documents 8and 9, the inventors attempted further study. As a result, the inventorshave conceived that recovery and storage of hydrogen as well asutilization of hydrogen could be achieved more efficiently if the highlyconcentrated hydrogen could be recovered and stored simultaneously inaddition to purifying a biomass pyrolysis gas to recover hydrogen.However, if a high-pressure gas cylinder is used for storage as aconventional manner, it is not easy to handle it. Then, the inventorshave conceived to use a hydrogen occlusion alloy so that hydrogen isstored in a container filled with the hydrogen occlusion alloy. Theinventors found that if the container filled with the hydrogen occlusionalloy is preferably prepared as a cartridge which can be used as it isas a hydrogen storage container in an instrument equipped with a fuelcell utilizing hydrogen as fuel, the container in which hydrogen wasstored can be used as it is for a predetermined application, so that aprocess from purification of hydrogen to use thereof can be streamlinedvery efficiently. This finding led to the completion of the presentinvention.

That is, the invention relates to: (1) a method for recovering hydrogenfrom pyrolysis gas obtained by heat-treating biomass, comprising: afirst purification step in which gas mainly containing carbon dioxide isadsorbed and removed from the pyrolysis gas under increased pressures topurify the pyrolysis gas; and a second purification step in which, at apressure not higher than that in the first purification step, thepurified gas obtained from the first purification step is furtherpurified by adsorbing and removing gas containing carbon dioxide fromthe purified gas under increased pressure to recover a gas mainlycontaining hydrogen from the purified gas, and the method furthercomprising a hydrogen storage step in which the gas mainly containinghydrogen recovered in the second purification step is supplied to acontainer filled with a hydrogen occlusion alley so as to store highpurity hydrogen in the container.

Preferred aspects include: (2) The method for recovering hydrogenaccording to (1), wherein the container filled with the hydrogenocclusion alloy is of a cartridge type which can be used as it is as ahydrogen storage container in an instrument equipped with a fuel cellutilizing hydrogen as fuel;

(3) The method for recovering hydrogen according to (2), wherein theinstrument equipped with the fuel cell utilizing hydrogen as fuel isselected from a group consisting of: an automobile, a backup powersupply, a radio, a mobile phone, an unmanned airplane and a domesticthermoelectric supply system;

(4) The method for recovering hydrogen according to any one of (1) to(3), wherein the hydrogen occlusion alloy is one or more selected from agroup consisting of: LaNi₅, LaNi_(4.7)Al_(0.3), TiFe_(0.9)Mn_(0.1),MmNi_(4.15)Fe_(0.35), CaNi₅, TiCrV and Lm-Ni-based alloy;

(5) The method for recovering hydrogen according to any one of (1) to(4), wherein the pressure in the hydrogen storage step is 0.15 MPa to0.6 MPa;

(6) The method for recovering hydrogen according to any one of (1) to(4), wherein the pressure in the hydrogen storage step is 0.2 MPa to 0.6MPa;

(7) The method for recovering hydrogen according to any one of (1) to(4), wherein the pressure in the hydrogen storage step is 0.2 MPa to 0.5MPa;

(8) The method for recovering hydrogen according to any one of (1) to(7), wherein 2 or more containers filled with the hydrogen occlusionalloy are utilized in the hydrogen storage step, wherein: hydrogen inthe gas mainly containing hydrogen recovered in the second purificationstep is occluded in the hydrogen occlusion alloy in one container filledwith the hydrogen occlusion alloy and stored in the one container; thenthe container is switched to another container filled with the hydrogenocclusion alloy; and while hydrogen in the gas mainly containinghydrogen is occluded in the hydrogen occlusion alloy and stored in theanother container, the one container in which hydrogen has already bestored is removed and replaced with a new container filled with thehydrogen occlusion alloy so as to continue an operation of storinghydrogen.

(9) The method according to any one of (1) to (8), wherein 2 to 5containers filled with the hydrogen occlusion alloy are utilized in thehydrogen storage step;

(10) The method according to any one of (1) to (9), wherein thecontainer filled with the hydrogen occlusion alloy comprises equipmentfor cooling and/or heating;

(11) The method according to any one of (1) to (10), wherein thepressure in the first purification step is 0.15 MPa to 0.6 MPa;

(12) The method according to any one of (1) to (10), wherein thepressure in the first purification step is 0.2 MPa to 0.6 MPa;

(13) The method according to any one of (1) to (10), wherein thepressure in the first purification step is 0.2 MPa to 0.5 MPa;

(14) The method according to any one of (1) to (13), wherein thepressure in the second purification step is 0.15 MPa to 0.6 MPa;

(15) The method according to any one of (1) to (13), wherein thepressure in the second purification step is 0.2 MPa to 0.6 MPa;

(16) The method according to any one of (1) to (13), wherein thepressure in the second purification step is 0.2 MPa to 0.5 MPa;

(17) The method according to any one of (1) to (16), wherein thepressure in the first purification step is 0.15 MPa to 0.6 MPa and thepressure in the second purification step is 0.15 MPa to 0.6 MPa;

(18) The method according to any one of (1) to (16), wherein thepressure in the first purification step is 0.2 MPa to 0.6 MPa and thepressure in the second purification step is 0.2 MPa to 0.6 MPa;

(19) The method according to any one of (1) to (16), wherein thepressure in the first purification step is 0.2 MPa to 0.6 MPa and thepressure in the second purification step is 0.2 MPa to 0.5 MPa;

(20) The method according to any one of (1) to (19), wherein any oftemperatures in the first purification step, the second purificationstep and the hydrogen storage step are in a range of 0 to 100° C.;

(21) The method according to any one of (1) to (19), wherein any oftemperatures in the first purification step, the second purificationstep and the hydrogen storage step are in a range of 10 to 40° C.;

(22) The method according to any one of (1) to (19), wherein any oftemperatures in the first purification step, the second purificationstep and the hydrogen storage step are ambient temperature;

(23) The method for recovering hydrogen according to any one of (1) to(22), wherein gas mainly containing carbon dioxide adsorbed and removedin the first purification step is recovered;

(24) The method for recovering hydrogen according to any one of (1) to(23), wherein a differential pressure between the pressure in the firstpurification step and the pressure in the second purification step is 0to 0.45 MPa;

(25) The method for recovering hydrogen according to any one of (1) to(23), wherein a differential pressure between the pressure in the firstpurification step and the pressure in the second purification step is 0to 0.4 MPa;

(26) The method for recovering hydrogen according to any one of (1) to(23), wherein a differential pressure between the pressure in the firstpurification step and the pressure in the second purification step is 0to 0.3 MPa;

(27) The method for recovering hydrogen according to any one of (1) to(23), wherein a differential pressure between the pressure in the firstpurification step and the pressure in the second purification step is 0to 0.2 MPa;

(28) The method for recovering hydrogen according to any one of (1) to(23), wherein a differential pressure between the pressure in the firstpurification step and the pressure in the second purification step is 0to 0.1 MPa;

(29) The method for recovering hydrogen according to any one of (1) to(28), wherein: the first purification step comprises two or moreadsorption columns; the gas mainly containing carbon dioxide is adsorbedand removed in one adsorption column to purify the pyrolysis gas; thenthe adsorption column is switched to the other column, in which the gasmainly containing carbon dioxide is adsorbed and removed to purify thepyrolysis gas; meanwhile, in the one adsorption column which has alreadyadsorbed and removed the gas mainly containing carbon dioxide, theadsorbed and removed gas mainly containing carbon dioxide is desorbedand recovered by reducing the pressure in the adsorption column;

(30) The method according to any one of (1) to (29), wherein the firstpurification step comprises 2 to 5 adsorption columns;

(31) The method for recovering hydrogen according to any one of (1) to(30), wherein: the second purification step comprises two or moreadsorption columns; the gas containing carbon dioxide is adsorbed andremoved in one adsorption column to purify the pyrolysis gas purified inthe first purification stage; then the adsorption column is switched tothe other column, in which the gas containing carbon dioxide is adsorbedand removed to further purify the pyrolysis gas purified in the firstpurification stage; meanwhile, in the one adsorption column which hasalready adsorbed and removed the gas containing carbon dioxide, theadsorbed and removed gas containing carbon dioxide is desorbed andrecovered by reducing the pressure in the adsorption column;

(32) The method according to any one of (1) to (31), wherein the secondpurification step comprises 2 to 5 adsorption columns;

(33) The method according to any one of (1) to (32), wherein both thefirst purification step and the second purification step are configuredby a pressure swing adsorption (PSA) apparatus;

(34) The method according to any one of (1) to (33), wherein anadsorbent used for adsorbing and removing the gas mainly containingcarbon dioxide in the first purification step is one or more selectedfrom a group consisting of imogolite, amorphous aluminum silicate,activated carbon, zeolite and activated alumina;

(35) The method according to any one of (1) to (33), wherein theadsorbent used for adsorbing and removing the gas mainly containingcarbon dioxide in the first purification step is imogolite;

(36) The method according to any one of (1) to (35), wherein anadsorbent used for adsorbing and removing the gas containing carbondioxide in the second purification step is one or more selected from agroup consisting of imogolite, amorphous aluminum silicate, activatedcarbon, zeolite and activated alumina;

(37) The method according to any one of (1) to (35), wherein anadsorbent used for adsorbing and removing the gas containing carbondioxide in the second purification step is activated carbon or zeolite;

(38) The method according to any one of (1) to (37), wherein the gascontaining carbon dioxide adsorbed and removed in the secondpurification step is gas containing hydrogen, carbon dioxide andmethane;

(39) The method according to any one of (1) to (38), wherein thepyrolysis gas encompasses gas obtained by steam-reforming the pyrolysisgas obtained by heat-treating the biomass.

Effects of Invention

The hydrogen recovery method of the present invention not onlysubstantially reduces operating costs such as power consumption but alsocontributes to substantial reduction in apparatus costs, because it canrecover highly concentrated hydrogen gas under a relatively lowpressure, and moreover it does not require to combine special agents orapparatuses which have been used in prior art, e.g., adsorbents,separation membranes, etc. Additionally, the method can remarkablyenhance safety in operation, because the operating pressure is low. Inaddition, the method allows overall reduction in power consumption, andthus it can also indirectly contribute to reduction in carbon dioxidegeneration. Above all, in the method for recovering hydrogen accordingthe present invention, recovery and storage of hydrogen as well asutilization of hydrogen can be achieved very efficiently becausehydrogen could be recovered and stored simultaneously, and hydrogen isstored in a cartridge-type container which can be used as it is as ahydrogen storage container in an instrument equipped with a fuel cell.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flow diagram of a hydrogen recovery method of thepresent invention; and

FIG. 2 is a schematic view of one embodiment of a hydrogen purificationand storage apparatus (first purification step, second purification stepand hydrogen storage step) which may be used in the hydrogen recoverymethod of the present invention.

DESCRIPTION OF EMBODIMENTS

The hydrogen recovery method of the present invention comprises: a firstpurification step for adsorbing and removing gas mainly containingcarbon dioxide from pyrolysis gas obtained by heat-treating biomass; asecond purification step for adsorbing and removing gas containingcarbon dioxide from the purified gas obtained in the first purificationstep; and a hydrogen storage step in which high-purity hydrogen from thegas mainly containing hydrogen recovered in the second purification stepis occluded and stored in the hydrogen occlusion alloy. As shown in FIG.1, biomass (a) is charged into a biomass heat-treating step (III) (heattreatment apparatus) to produce pyrolysis gas (b). Herein, the pyrolysisgas (b) may be gas obtained by further steam-reforming the pyrolysis gasobtained by heat-treating the biomass, i.e., reformed gas. Subsequently,the produced pyrolysis gas (b) is charged into a first purification step(I), wherein gas (e) mainly containing carbon dioxide contained in thepyrolysis gas (b), e.g., gas mainly containing carbon dioxide andcontaining carbon monoxide, methane, hydrogen and the like as othercomponents is adsorbed and removed by an adsorbent. Purified gas (c)from which the gas (e) mainly containing carbon dioxide has been removed(hereinafter referred to as “first purified gas” in some cases) issubsequently charged into a second purification step (II), wherein gas(f) containing carbon dioxide, e.g., gas containing hydrogen, carbondioxide and methane, as well as optionally carbon monoxide and the likeis adsorbed and removed by an adsorbent. On the other hand, the gas (e)mainly containing carbon dioxide adsorbed in the first purification step(I) and the gas (f) containing carbon dioxide adsorbed in the secondpurification step (II) are desorbed from the adsorbents and separatelyrecovered. The gas (d) mainly containing hydrogen from which the gas (e)mainly containing carbon dioxide and the gas (f) containing carbondioxide have been removed (hereinafter referred to as “second purifiedgas” in some cases) is subsequently charged into a hydrogen storage step(IV), wherein the hydrogen occlusion alloy occludes almost only hydrogenso as to store high-purity hydrogen (h) and discharge a gas (g)containing carbon dioxide (hereinafter referred to as “hydrogenocclusion step off-gas” in some cases). Herein, the gas (e) mainlycontaining carbon dioxide refers to gas containing carbon dioxide as ahighest volume ratio in the gas, and besides carbon dioxide, it containscarbon monoxide, methane and hydrogen, and it may further contain asulfur compound gas such as hydrogen sulfide and carbonyl sulfide, anitrogen compound gas and the like. The gas (f) containing carbondioxide refers to gas containing hydrogen, carbon dioxide and methane,and it may further contain carbon monoxide, sulfur compound gas,nitrogen compound gas and the like. In addition, the hydrogen occlusionstep off-gas (g) has a largest volume ratio of carbon dioxide and maycontain methane as well as very small amounts of hydrogen and carbonmonoxide.

In the first purification step, carbon dioxide (gas mainly containingcarbon dioxide) is primarily adsorbed and removed from the biomasspyrolysis gas. Also, water in the biomass pyrolysis gas can be adsorbedand removed. The adsorption and removal are carried out under increasedpressure. The pressure has an upper limit of preferably 0.6 MPa, or morepreferably 0.5 MPa, and a lower limit of preferably 0.15 MPa, or morepreferably 0.2 MPa. A pressure below the lower limit is unfavorable,because the adsorbability of the adsorbent is lowered. In addition,although the gas mainly containing carbon dioxide can be adsorbed anddesorbed even at a pressure lower than the lower limit, the adsorptionlayer becomes excessive because a large amount of adsorbent is requireddue to lowered adsorbability. On the other hand, a pressure above theupper limit is unfavorable because a great deal of power is required forpressurization. Operating temperature at the first purification step,i.e., operating temperature for concurrently adsorbing carbon dioxide,carbon monoxide and a hydrocarbon gas such as methane is preferably 0 to100° C., more preferably 10 to 40° C. The operation is typically carriedout at ambient temperature.

As the adsorbent in the first purification step, preferably one or moreadsorbents selected from a group consisting of imogolite, amorphousaluminum silicate, activated carbon, zeolite and activated alumina, ormore preferably one or more adsorbents selected from a group consistingof imogolite, amorphous aluminum silicate, activated carbon and zeoliteare used. These adsorbents can be used as a single layer, or laminatedmultiple layers. More preferably, a single layer of imogolite or asingle layer of amorphous aluminum silicate is used. Herein, as theamorphous aluminum silicate, a synthetic amorphous aluminum silicate(synthetic imogolite) is preferably used. As the synthetic amorphousaluminum silicate, a commercial product, e.g., Hasclay (registeredtrademark) manufactured by TODA KOGYO CORP. can be used.

In the first purification step, 30 to 80 vol % of carbon dioxide in thebiomass pyrolysis gas can be removed. Since 20 to 40 vol % of carbondioxide is normally present in the biomass pyrolysis gas, thepurification in the first purification step can reduce the volume ofcarbon dioxide in the biomass pyrolysis gas to about 5 to 35 vol %.Carbon dioxide and other gases (gas mainly containing carbon dioxide)adsorbed and removed as described above in the first purification stepare desorbed and recovered from the adsorbent by lowering the pressurein the column to normal pressure.

The first purification step is preferably configured by a pressure swingadsorption (PSA) apparatus. In the first purification step, preferably 2or more, more preferably 2 to 5 adsorption columns (PSA adsorptioncolumns) filled with the adsorbent are installed.

The operating method in the first purification step mainly includes thefollowing two types. One method is a so-called continuous method. Thebiomass pyrolysis gas is pressurized to the above-mentioned pressure;the gas kept at a constant pressure is continuously passed through oneadsorption column for a predetermined time; in the adsorption column,the gas mainly containing carbon dioxide and optionally water areadsorbed by the adsorbent and removed; and unadsorbed gas, i.e.,purified gas is continuously withdrawn. Subsequently, the column isswitched to another adsorption column; the biomass pyrolysis gas iscontinuously passed therethrough for a predetermined time in the samemanner as described above; in the other adsorption column, the gasmainly containing carbon dioxide is adsorbed and removed; and purifiedgas is continuously withdrawn. At this time, the one adsorption columnin which the adsorbing operation has been already completed isdepressurized, and the adsorbed gas mainly containing carbon dioxide isdesorbed and recovered. Thereafter, in the one adsorption column, theadsorbent is regenerated if necessary, and the biomass pyrolysis gas ispassed therethrough again. In this method, these operations aresequentially repeated.

In the above continuous method, the switching from the one adsorptioncolumn to another adsorption column is carried out within a time duringwhich the adsorbability is not reduced, in consideration of the time ofreducing the adsorbability (breakthrough time) of carbon dioxide and thelike for the adsorbent charged into the one adsorption column. The timedepends on the amount of the treated biomass pyrolysis gas, the amountof carbon dioxide and the like therein, the capacity of the adsorptioncolumn, the kind and amount of the adsorbent charged into the column,and the like, but it is typically on the order of 2 to 30 minutes.Typically, the time is preliminarily determined in accordance withexperiments by measuring the concentration of carbon dioxide in theremoved first purified gas and the concentration of carbon dioxide inthe gas recovered through adsorption and removal in the firstpurification step, so that the concentration of carbon dioxide in theremoved first purified gas is minimized. Alternatively or additionally,the concentration of hydrogen or carbon dioxide in the first purifiedgas flowing out from the adsorption column is continuously orintermittently measured, and it is possible to switch one adsorptioncolumn to another adsorption column when the hydrogen concentration inthe first purified gas decreases to a concentration lower than apredetermined value or when the concentration of carbon dioxide exceedsa predetermined value. Subsequently, after charge of the biomasspyrolysis gas into the other adsorption column is started, in the oneadsorption column which has already adsorbed and removed the gas mainlycontaining carbon dioxide, the adsorbed and removed gas mainlycontaining carbon dioxide is desorbed and recovered from the adsorbentby lowering the pressure in the column preferably to around atmosphericpressure.

Another method is a so-called semi-continuous method. The biomasspyrolysis gas is pressurized to the above pressure and charged into oneadsorption column; the gas is kept at the pressure for a predeterminedtime; and in the adsorption column, the gas mainly containing carbondioxide and optionally water are adsorbed by the adsorbent and removed.Subsequently, the column is switched to another adsorption column, andthe biomass pyrolysis gas is charged into the other column and kept fora predetermined time in the same manner as described above. In the otheradsorption column, the gas mainly containing carbon dioxide is adsorbedand removed. After switching to the other adsorption column, the oneadsorption column in which the adsorbing operation has been alreadycompleted is depressurized to a predetermined pressure, and theunadsorbed gas, i.e., the purified gas is withdrawn. Then, the oneadsorption column is depressurized, and the adsorbed gas mainlycontaining carbon dioxide is desorbed and recovered. Thereafter, in theone adsorption column, the adsorbent is regenerated if necessary, andthe biomass pyrolysis gas is charged and kept again. In this method,these operations are sequentially repeated.

In the above semi-continuous method, the switching from the oneadsorption column to another adsorption column is carried out within atime which is sufficient for the charged adsorbent adsorbs carbondioxide and the like, in consideration of the relationship between theadsorbability of carbon dioxide and the like for the adsorbent chargedinto the one adsorption column and the amount of carbon dioxide and thelike in the charged biomass pyrolysis gas. The time depends on theamount of the charged biomass pyrolysis gas, the amount of carbondioxide and the like therein, the capacity of the adsorption column, thekind and amount of the adsorbent charged into the column, and the like,but it is typically on the order of 2 to 30 minutes. Typically, the timeis previously determined in accordance with experiments by measuring theconcentration of carbon dioxide in the adsorbed and removed firstpurified gas and the concentration of carbon dioxide in the gasrecovered through adsorption and removal in the first purification step,so that the concentration of carbon dioxide in the removed firstpurified gas is minimized. Alternatively or additionally, theconcentration of hydrogen or carbon dioxide in the gas in the adsorptioncolumn is continuously or intermittently measured, and it is possible toswitch one adsorption column to another adsorption column when thehydrogen concentration in the gas in the adsorption column exceeds apredetermined value or when the concentration of carbon dioxidedecreases to a concentration lower than a predetermined value.Subsequently, after the adsorption operation in the one adsorptioncolumn is completed, the pressure in the one adsorption column isdepressurized to a predetermined pressure, and the unadsorbed gas, i.e.,the purified gas is withdrawn. The predetermined pressure ispreliminarily determined in accordance with experiments within such arange that the adsorbed and removed gas such as carbon dioxide and thelike would not desorbed, in consideration of the kind, pore volume,specific surface area and the like of the charged adsorbent, the maximumpressure in the adsorption operation, the operating temperature, and thelike. Typically, the predetermined pressure is on the order of 0.15 to0.3 MPa. Subsequently, the adsorbed and removed gas mainly containingcarbon dioxide is desorbed and recovered from the adsorbent by loweringthe pressure in the one adsorption column preferably to aroundatmospheric pressure.

As described above, the purified gas (first purified gas) obtained fromthe first purification step is charged into the second purification stepwith keeping or reducing the pressure in the first purification step. Atthis time, a container may be provided between the first purificationstep and the second purification step, the first purified gas is oncedepressurized to preferably 0.1 to 0.3 MPa, more preferably 0.1 to 0.2MPa, and then pressurized again by a pressurizing apparatus, e.g., acompressor, so that the gas can be charged into the second purificationstep.

In the second purification step, gases containing carbon dioxide, e.g.,gases containing hydrogen, carbon dioxide and methane, and optionallycarbon monoxide and the like are adsorbed and removed from the firstpurified gas. In addition, if a sulfur compound gas, a nitrogen compoundgas or the like is contained, they are also adsorbed and removed. In thesecond purification step, the adsorption and removal of the gascontaining carbon dioxide are carried out under increased pressure. Thepressure has an upper limit of preferably 0.6 MPa, or more preferably0.5 MPa, and a lower limit of preferably 0.15 MPa, or more preferably0.2 MPa. A pressure below the lower limit is unfavorable, because theadsorbability of the adsorbent is lowered. In addition, although gasother than hydrogen, e.g., mainly methane, carbon monoxide or the likecan be adsorbed and desorbed even at a pressure lower than the lowerlimit, the adsorption layer becomes excessive because a large amount ofadsorbent is required due to lowered adsorbability. On the other hand, apressure above the upper limit is unfavorable because a great deal ofpower is required for pressurization. The differential pressure betweenthe pressure for adsorbing and removing the gas mainly containing carbondioxide in the first purification step and the pressure for adsorbingand removing the gas containing carbon dioxide in the secondpurification step is preferably 0 to 0.45 MPa, more preferably 0 to 0.4MPa, even more preferably 0 to 0.3 MPa, most preferably 0 to 0.1 MPa.Such a pressure difference is adopted, so that gas can be efficientlyadsorbed and removed in the first and second purification steps. Inaddition, the operating temperature in the second purification step isthe same as that in the first purification step, and is preferably 0 to100° C., more preferably 10 to 40° C. The second purification step isusually carried out at ambient temperature.

As the adsorbent in the second purification step, one or more adsorbentsselected from a group consisting of imogolite, amorphous aluminumsilicate, activated carbon, activated alumina and zeolite are preferablyused. They can be used as a single layer, or laminated multiple layers.More preferably, a single layer of activated carbon or zeolite is used.

The second purification step is preferably configured by a conventionalhydrogen pressure swing adsorption (hydrogen PSA) apparatus used forrecovering high-purity hydrogen. In the second purification step,preferably 2 or more, more preferably 2 to 5 adsorption columns(hydrogen PSA adsorption column) filled with the adsorbent areinstalled.

The operation method in the second purification step may also includetwo methods, i.e., a continuous method and a semi-continuous method,similarly to the operation method in the first purification step. All ofoperations such as adsorption and switching of the adsorption column inthe continuous method and the semi-continuous method are carried out inthe same manner as described with respect to the first purificationstep.

In the hydrogen recovery method of the present invention, hydrogenhaving a purity of 90 vol % or higher can be recovered by combining thefirst purification step and the second purification step as describedabove.

As described above, the purified gas (second purified gas) obtained fromthe second purification step is charged into the hydrogen storage stepwith keeping, increasing or reducing the pressure in the secondpurification step. At this time, a container may be provided between thesecond purification step and the hydrogen storage step, the secondpurified gas is once depressurized to preferably 0.1 to 0.3 MPa, morepreferably 0.1 to 0.2 MPa, and then pressurized again by a pressurizingapparatus, e.g., a compressor, so that the gas can be charged into thehydrogen storage step.

In the hydrogen storage step, the hydrogen occlusion alloy occludes andstores almost only hydrogen contained in the second purified gas, and agas containing carbon dioxide (hydrogen occlusion step off-gas) isdischarged. In the hydrogen storage step, occlusion of hydrogen into thehydrogen occlusion alloy is carried out under increased pressure. Thepressure depends on the hydrogen gas dissociation equilibrium pressureand has an upper limit of preferably 0.6 MPa, or more preferably 0.5MPa, and a lower limit of preferably 0.15 MPa, or more preferably 0.2MPa. A pressure below the lower limit is unfavorable because theocclusion ability of the hydrogen occlusion alloy is lowered. On theother hand, a pressure above the upper limit is unfavorable because agreat deal of power is required for pressurization. In addition, theoperating temperature in the hydrogen storage step is the same as thatin the first and second purification steps, and is preferably 0 to 100°C., more preferably 10 to 40° C. The hydrogen storage step is usuallycarried out at ambient temperature.

The hydrogen occlusion alloy charged into the container in the hydrogenstorage step is not particularly limited, but preferably, those capableof occlude and release hydrogen at a normal temperature are used.Examples include LaNi₅, LaNi_(4.7)Al_(0.3), TiFe_(0.9)Mn_(0.1),MmNi_(4.15)Fe_(0.35), CaNi₅, TiCrV, Lm-Ni-based alloy and the like andpreferably include LaNi₅, CaNi₅, TiCrV, Lm-Ni-based alloy and the likewhich can occlude and release hydrogen at a normal temperature. They canbe used as a single layer or a stack of multiple layers. Morepreferably, a single layer of Lm-Ni-based alloy is used. Here, Mm meansmisch metal and Lm means lanthanum-rich misch metal.

Similar to the operating method in the first and second purificationstep, the operating method in the hydrogen storage step mainly includesa continuous method and a semi-continuous method. The continuous methodis preferably used. In the continuous method, the second purified gas ispressurized to the above-mentioned pressure; the gas kept at a constantpressure is continuously passed through one container filled with thehydrogen occlusion alloy for a predetermined time; in the containerfilled with the hydrogen occlusion alloy, the hydrogen occlusion alloyoccludes almost only hydrogen, and the gas which has not been occluded,i.e., the hydrogen occlusion step off-gas which mainly contains carbondioxide is separated from hydrogen and continuously withdrawn.Subsequently, the container is switched to another container filled withthe hydrogen occlusion alloy; the second purified gas is continuouslypassed therethrough for a predetermined time in the same manner asdescribed above; in the another adsorption column, the hydrogenocclusion alloy occludes almost only hydrogen and the hydrogen occlusionstep off-gas which mainly contains carbon dioxide is separated fromhydrogen and continuously withdrawn. Thus, almost only hydrogen in thesecond purified gas is occluded in the hydrogen occlusion alloy andstored in the container. The occluded hydrogen can be recovered bydepressurize the container in which the occluding operation has beenalready completed so as to make it release the occluded hydrogen. Thecontinuous operation can be maintained by repeating these operations.

In the above continuous method, the switching from the one containerfilled with the hydrogen occlusion alloy to another container filledwith the hydrogen occlusion alloy is carried out within a time duringwhich the occlusion ability is not reduced, in consideration of the timeof reducing the ability of the hydrogen occlusion alloy charged into theone container to occlude hydrogen. The time depends on the amount of thetreated second purified gas, the amount of hydrogen therein, thecapacity of the container, the kind and amount of the hydrogen occlusionalloy charged into the container, and the like, but it is typically onthe order of 1 to 30 minutes. Typically, the time is preliminarilydetermined in accordance with experiments by measuring the concentrationof hydrogen in the hydrogen occlusion step off-gas after the occlusionof hydrogen and the concentration of hydrogen in the gas occluded intothe hydrogen occlusion alloy in the hydrogen occlusion step and thenrecovered, so that the concentration of hydrogen in the hydrogenocclusion step off-gas is minimized. Alternatively or additionally, theconcentration of hydrogen and/or carbon dioxide in the hydrogenocclusion step off-gas flowing out from the container filled with thehydrogen occlusion alloy is continuously or intermittently measured, andit is possible to switch one container to another container when thehydrogen concentration in the hydrogen occlusion step off-gas increasesto a concentration not less than a predetermined value or when theconcentration of carbon dioxide decreases to a concentration not morethan a predetermined value. Subsequently, after charge of the secondpurified gas into the another container filled with the hydrogenocclusion alloy is started, in the one container in which the hydrogenocclusion alloy has already occluded hydrogen, the occluded hydrogen isreleased and recovered from the hydrogen occlusion alloy by lowering thepressure in the container preferably to around atmospheric pressure.

The above-described continuous method is suitable for a case wherehydrogen stored in the container filled with the hydrogen occlusionalloy is utilized at that place, i.e., at the vicinity of an apparatusfor carrying out the method of present invention. In this case, thecontainer filled with the hydrogen occlusion alloy is mounted in theapparatus and not moved. Therefore, a column-type container ispreferably used. Hydrogen once stored in the container filled with thehydrogen occlusion alloy is immediately withdrawn and transferred viapipes or the like for use. More preferably, the container filled withthe hydrogen occlusion alloy is a cartridge-type container which can beused as it is as a hydrogen storage container in an instrument equippedwith a fuel cell utilizing hydrogen as fuel. In this case, a containerin which the hydrogen occlusion alloy has completed the occlusion ofhydrogen so that hydrogen is stored therein is removed from theapparatus without depressurization, and then a new container filled withthe hydrogen occlusion alloy is attached as a replacement. Thus, thecontinuous operation of the apparatus is achieved. Then, the removedcontainer in which hydrogen is stored is used for a predeterminedapplication immediately or after storage. The container filled with thehydrogen occlusion alloy is designed to have the same shape or the likeas that of a hydrogen storage container in an instrument equipped with afuel cell. The instrument equipped with the fuel cell includes:automobile, a backup power supply, a radio, a mobile phone such as asmartphone, an unmanned airplane such as a drone, a domesticthermoelectric supply system, and the like, for example.

Methods and apparatuses for producing the pyrolysis gas (b) byheat-treating the biomass (a) are known. For example, the followingmethod can be used for example: a method comprising: heat-treatingbiomass such as organic waste at 500 to 600° C. under a non-oxidizingatmosphere; mixing the generated pyrolysis gas with steam at 900 to1,000° C.; and purifying the resulting reformed gas to recover hydrogen(Patent Document 10); or a method for gasifying organic waste,comprising: heat-treating organic waste at 400 to 700° C. under anon-oxidizing atmosphere; mixing the generated pyrolysis gas with steamat 700 to 1,000° C.; and purifying the resulting reformed gas to producehydrogen-containing gas, wherein: purifying the reformed gas is carriedout by passing the reformed gas through a layer containing aluminumoxide and/or a formed article thereof and kept at 400 to 700° C. andthen further passing the resulting gas through a layer containing one ormore substances selected from a group consisting of zinc oxide, ironoxide, calcium oxide and formed articles thereof and kept at 350 to 500°C.; and subsequently the reformed gas after the purification is passedthrough a shift reaction catalyst layer at 200 to 500° C. (PatentDocument 11). As the pyrolysis gas (b), pyrolysis gas before steamreforming obtained in the above-mentioned method or the like can beused, but it is preferable to use gas in which hydrogen concentration isincreased by steam-reforming the pyrolysis gas. Herein, although thebiomass (a) is not particularly limited as long as it is described inPatent Documents 9 and 10, it is exemplified by a waste material frompalm tree (empty fruit bunch: EFB, EFB fiber, palm kernel shell),coconut shell, coconut husk, a waste material from Jatropha tree, anunused waste wood from forests, a sawmill waste from a sawmillingfactory, waste paper, rice straw, rice husk, food residue from a foodfactory, algae, sewage sludge, organic sludge, and the like.

The hydrogen recovery method of the present invention may furtherinclude a purification step of other substances as long as the effect ofthe present invention is not impaired. For example, when biomasscontaining a radioactive substance such as cesium is used, a step ofadsorbing and removing the radioactive substance such as cesium can beprovided prior to the first purification step for adsorbing and removingcarbon dioxide of the present invention. Thereby, the method can also beused for recovering hydrogen from biomass containing radioactive wasteor the like.

Hereinafter, the present invention will be described in more detail withreference to Examples, but the present invention is not limited by theseExamples.

EXAMPLES

The biomass raw material used in Examples is as follows.

As the biomass raw material, pencil manufacture waste wood (manufacturedby KITA-BOSHI PENCIL CO., LTD., derived from an incense cedar native ofCA, USA) was used. The pencil manufacture waste wood was in a form ofsawdust. The characteristics of the pencil manufacture waste wood areshown in Table 1.

TABLE 1 Proximate Analysis Volatile Matter 88.23 mass % Ash 0.37 mass %Fixed Carbon 11.40 mass % Elementary Analysis Carbon 50.90 mass %Hydrogen 7.30 mass % Oxygen 41.62 mass % Nitrogen 0.13 mass % Sulfur0.03 mass % Chlorine 0.02 mass % Lower Heating Value 18.4 MJ/kg

In Table 1, the proximate analysis values were measured in accordancewith JIS M8812, and the elementary analysis values were measured inaccordance with JIS M8819. Note that, in the elementary analysis values,“sulfur” and “chlorine” were measured by combustion-ion chromatography[combustion unit: Automatic Quick Fumace AQF-100 (trademark)manufactured by Mitsubishi Chemical Analytech Co., Ltd., gas-absorbingunit: Gas Absorptior Unite GA-100 (trademark) manufactured by MitsubishiChemical Analytech Co., Ltd., detection unit: an ion chromatograph IonChromatography System ICS-1000 (trade name) manufactured by DionexCorporation]. Note that “oxygen” was calculated by subtracting theamount of elements other than oxygen from 100 mass %. In addition, alower heating value was measured in accordance with JIS M8814. Herein,all the values are calculated on a dry mass basis.

Example 1

For pyrolysis and gas reforming of the biomass material, a cylindricalquartz tube having a diameter of 50 mm and height of 500 mm was used asa pyrolysis reactor, and a cylindrical stainless tube having a diameterof 50 mm and height of 500 mm was used as a reforming reactor. About 1gram (dry weight) of pencil manufacture waste wood was charged into thepyrolysis reactor, and pyrolysis of the pencil manufacture waste woodwas carried out at 550° C. with passing argon gas therethrough at 50ml/min. Subsequently, the total amount of the resulting pyrolysis gaswas fed into the reforming reactor, and at the same time, distilledwater was fed to a heating zone of the reforming reactor at a rate of0.04 ml/min and evaporated to produce water vapor, and the pyrolysis gaswas reformed at 950° C. Thereby, 8.25 L of mixed gas of argon gas andreformed gas was obtained (0° C. and 1 atm basis). Herein, the mixed gascontained 3.18 L of reformed gas and 5.07 L of argon gas. The mixed gaswas analyzed using gas chromatography [GC-14A (trademark) manufacturedby Shimadzu Corporation, carrier gas: argon]. The composition of thereformed gas contained in the mixed gas is as shown in the followingTable 2. The hydrogen concentration was 61.42 vol %, and on the otherhand, the carbon dioxide concentration was 23.02 vol %, the carbonmonoxide concentration was 8.89 vol %, and the methane concentration was6.67 vol %. In the analysis using the gas chromatography, since argonwas used as a carrier gas, argon was not detected in the mixed gassubjected for the analysis. Subsequently, a gas purification test wascarried out, in which hydrogen gas was recovered using thepost-pyrolysis reformed gas obtained as described above. In addition,the reformed gas was repeatedly produced in order to obtain a gas amountcapable of sufficiently performing the gas purification test describedbelow.

TABLE 2 Component Concentration(vol %) Hydrogen 61.42 Carbon Dioxide23.02 Carbon Monoxide 8.89 Methane 6.67

As the hydrogen recovery and storage apparatus, one shown in FIG. 2 wasused. In the first purification step (A), four adsorption columns (11,12, 13, 14) were used with being connected in parallel. All of the fouradsorption columns were made of stainless steel (SUS 304), all of whichwere cylindrical with an inner diameter of 40 mm and height of 300 mm.Each adsorption column was filled with about 60 g of synthetic imogolite(HASClay Gill (trademark) manufactured by TODA KOGYO CORP.) as anadsorbent. The synthetic imogolite used had a pore volume of 1 cm3/g anda specific surface area of about 500 m2/g.

In the second purification step (B), four adsorption columns (21, 22,23, 24) were used with being connected in parallel. The materials, sizesand shapes of these adsorption columns were the same as those of theadsorption columns used in the first purification step (A). Eachadsorption column was filled with about 120 g of activated carbon(activated carbon Shirasagi X2M (trademark) manufactured by JapanEnviroChemicals, Limited) as an adsorbent.

In the hydrogen storage step (C), four adsorption columns (101, 102,103, 104) were used with being connected in parallel. These adsorptioncolumns were made of stainless steel (SUS 304) and were cylindrical withan inner diameter of 10 mm and height of 40 mm. Each adsorption columnwas equipped with an outer cylinder and a pipe therein in which coolingwater or heating water can be circulated. Each adsorption column wasfilled with about 100 g of hydrogen occlusion alloy, Lm-Ni-based alloy(hydrogen occlusion alloy manufactured by Japan Metals & Chemicals Co.,Ltd.).

As shown in FIG. 2, intermediate tanks (31) and (32) were installedbetween the first purification step (A) and the second purification step(B), and between the second purification step (B) and the hydrogenstorage step (C), respectively. In this example, as the intermediatetanks (31) and (32), a gas bag made of natural rubber having an internalvolume of 10 L was used.

As described above, the post-pyrolysis reformed gas obtained byheat-treating and reforming the pencil manufacture waste wood wascharged into the first adsorption column (11) in the first purificationstep (A). First, an inlet valve (VI11) of the first adsorption column(11) was opened, and an outlet valve (VO11) and an adsorption gaswithdrawal valve (VM11) were closed. At this time, all of inlet valves(VI12, VI13, VI14), outlet valves (VO12, VO13, VO14) and adsorption gaswithdrawal valves (VM12, VM13, VM14) of the second adsorption column(12), the third adsorption column (13) and the fourth adsorption column(14) were closed. The post-pyrolysis reformed gas was charged by acompressor (10) so that the internal pressure of the first adsorptioncolumn (11) was 0.5 MPa. The amount of mixed gas charged was about 2.56L (0° C., 1 atm). Then, the inlet valve (VI11) was closed, and the firstadsorption column (11) was held in this state for 5 minutes to adsorbthe gas mainly containing carbon dioxide. Subsequently, the outlet valve(VO11) was opened so as to reduce the pressure in the first adsorptioncolumn (11) to 0.2 MPa, and then the outlet valve (VO11) was closed. Thewithdrawn first purified gas (L1) was introduced into the intermediatetank (31). Subsequently, the adsorption gas withdrawal valve (VM11) wasopened so as to reduce the pressure in the first adsorption column (11)to 0.1 MPa, and then the adsorption gas withdrawal valve (VM11) wasclosed. The withdrawn gas mainly containing carbon dioxide was recoveredas the first purification step off-gas (L2). Then, argon gas wasintroduced and discharged from a cleaning gas inlet and outlet (notshown) into the first adsorption column (11) to regenerate theadsorbent.

In the above operation, the pressure in the first adsorption column (11)was adjusted to 0.5 MPa and the inlet valve (VI11) was closed, and atthe approximately same time, the inlet valve (VI12) of the secondadsorption column (12) was opened and the outlet valve (VO12) and theadsorption gas withdrawal valve (VM12) were closed. In this state, thepost-pyrolysis reformed gas was charged by the compressor (10) so thatthe internal pressure of the second adsorption column (12) was 0.5 MPa,and the same operation as in the first adsorption column (11) wascarried out in the second adsorption column (12). Thereafter, the sameoperations were sequentially repeated in the third adsorption column(13) and the fourth adsorption column (14), as well as in the firstadsorption column (11) and the second adsorption column (12) again, andgas purification in the first purification step (A) was almostsequentially continued. All of these operations were carried out atambient temperature.

The results of analyzing the post-purification gas (first purified gas(L1)) in the first purification step (A) using gas chromatography[GC-14A (trademark) manufactured by Shimadzu Corporation, carrier gas:argon] are as shown in the following Table 3, and the hydrogenconcentration was increased to 89.70 vol %, meanwhile the carbon dioxideconcentration was decreased to 7.97 vol %. In addition, the results ofanalyzing the first purification step off-gas (L2) mainly containingcarbon dioxide using gas chromatography [GC-14A (trademark) manufacturedby Shimadzu Corporation, carrier gas: argon] are as shown in thefollowing Table 4, and the carbon dioxide concentration was 51.07 vol %,and hydrogen, carbon monoxide and methane were detected in 48.93 vol %.

TABLE 3 Component Concentration(vol %) Hydrogen 89.70 Carbon Dioxide7.97 Carbon Monoxide 0.00 Methane 2.33

TABLE 4 Component Concentration(vol %) Hydrogen 8.74 Carbon Dioxide51.07 Carbon Monoxide 25.44 Methane 14.75

The first purified gas (L1) withdrawn from the first purification step(A) was introduced into the intermediate tank (31) and depressurized toabout 0.1 MPa. Subsequently, the first purified gas (L1) was chargedinto a first adsorption column (21) of the second purification step (B).First, an inlet valve (VI21) of the first adsorption column (21) wasopened, and an outlet valve (VO21) and an adsorption gas withdrawalvalve (VM21) were closed. At this time, all of inlet valves (VI22, VI23,VI24), outlet valves (VO22, VO23, VO24) and adsorption gas withdrawalvalves (VM22, VM23, VM24) of the second adsorption column (22), thethird adsorption column (23) and the fourth adsorption column (24) wereclosed. The first purified gas (L1) was charged by a compressor (20) sothat the internal pressure of the first adsorption column (21) was 0.4MPa. Then, the inlet valve (VI21) was closed, and the first adsorptioncolumn (21) was held in this state for 5 minutes to adsorb the gascontaining carbon dioxide. Subsequently, the outlet valve (VO21) wasopened so as to reduce the pressure in the first adsorption column (21)to 0.2 MPa, and then the outlet valve (VO21) was closed so as towithdraw the second purified gas (L3). Subsequently, the adsorption gaswithdrawal valve (VM21) was opened so as to reduce the pressure in thefirst adsorption column (21) to 0.1 MPa, and then the adsorption gaswithdrawal valve (VM21) was closed. The withdrawn gas containing carbondioxide was recovered as the second purification step off-gas (L4).Then, argon gas was introduced and discharged from a cleaning gas inletand outlet (not shown) into the first adsorption column (21) toregenerate the adsorbent.

In the above operation, the pressure in the first adsorption column (21)was adjusted to 0.4 MPa and the inlet valve (VI21) was closed, and atthe approximately same time, the inlet valve (VI22) of the secondadsorption column (22) was opened and the outlet valve (VO22) and theadsorption gas withdrawal valve (VM22) were closed. In this state, thefirst purified gas (L1) was charged by the compressor (20) so that theinternal pressure of the second adsorption column (22) was 0.4 MPa, andthe same operation as in the first adsorption column (21) was carriedout in the second adsorption column (22). Thereafter, the sameoperations were sequentially repeated in the third adsorption column(23) and the fourth adsorption column (24), as well as as in the firstadsorption column (21) and the second adsorption column (22) again, andgas purification in the second purification step (B) was almostsequentially continued. All of these operations were carried out atambient temperature.

The results of analyzing the post-purification gas (second purified gas(L3)) in the second purification step (B) using gas chromatography[GC-14A (trademark) manufactured by Shimadzu Corporation, carrier gas:argon] are as shown in the following Table 5, and the hydrogenconcentration was increased to 91.78 vol %, meanwhile the carbon dioxideconcentration was decreased to 6.61 vol %. In addition, the results ofanalyzing the second purification step off-gas (L4) containing carbondioxide using gas chromatography [GC-14A (trademark) manufactured byShimadzu Corporation, carrier gas: argon] are as shown in the followingTable 6, and the carbon dioxide concentration was 10.44 vol %, andhydrogen, carbon monoxide and the like were detected in about 89.56 vol%.

TABLE 5 Component Concentration(vol %) Hydrogen 91.78 Carbon Dioxide6.61 Carbon Monoxide 0.00 Methane 1.62

TABLE 6 Component Concentration(vol %) Hydrogen 85.93 Carbon Dioxide10.44 Carbon Monoxide 0.00 Methane 3.63

The gas after purification in the second purification step (B) (secondpurified gas (L3)) was introduced into the intermediate tank (32) anddepressurized to about 0.1 MPa. Subsequently, the second purified gas(L3) was charged into a first adsorption column (101) of the hydrogenstorage step (C). First, an inlet valve (VI31) of the first adsorptioncolumn (101) was opened, and an outlet valve (VO31) and an occlusion gaswithdrawal valve (VM31) were closed. At this time, all of inlet valves(VI32, VI33, VI34), outlet valves (VO32, VO33, VO34) and occlusion gaswithdrawal valves (VM32, VM33, VM34) of the second adsorption column(102), the third adsorption column (103) and the fourth adsorptioncolumn (104) were closed. The second purified gas (L3) was charged by acompressor (30) so that the internal pressure of the first adsorptioncolumn (101) was 0.5 MPa. Then, while keeping the internal pressure ofthe first adsorption column (101) at 0.5 MPa, the occlusion gaswithdrawal valve (VM31) was slightly opened to flow the second purifiedgas (L3) at a flow rate of about 0.08 L/min so that the first adsorptioncolumn (101) occluded hydrogen. Since heat is generated during theocclusion of hydrogen, the cooling water at about 20° C. was made topass through the pipe comprised in the outer cylinder of the firstadsorption column (101) so as to cool the first adsorption column (101).The first adsorption column (101) was held in this state for 5 minutesto adsorb hydrogen and withdraw a gas containing methane and carbondioxide through the occlusion gas withdrawal valve (VM31), so that thehydrogen occlusion step off-gas (L6) was obtained. Subsequently, theadsorption gas withdrawal valve (VM31) was closed and then the inletvalve (VI31) was closed so as to terminate the operation for occludinghydrogen into the hydrogen occlusion alloy charged in the firstadsorption column (101). Subsequently, the outlet valve (VO31) wasopened so as to reduce the pressure in the first adsorption column (101)to 0.1 MPa, and then the outlet valve (VO31) was closed so as to recoverthe gas (L5) occluded in the hydrogen occlusion alloy.

In the above operation, the inlet valve (VI31) of the first adsorptioncolumn (101) was closed, and at the approximately same time, the inletvalve (VI32) of the second adsorption column (102) was opened and theoutlet valve (VO32) and the occlusion gas withdrawal valve (VM32) wereclosed. In this state, the second purified gas (L3) was charged by thecompressor (30) so that the internal pressure of the second adsorptioncolumn (102) was 0.5 MPa, and the same operation as in the firstadsorption column (101) was carried out in the second adsorption column(102). Thereafter, the same operations were sequentially repeated in thethird adsorption column (103) and the fourth adsorption column (104), aswell as as in the first adsorption column (101) and the secondadsorption column (102) again, and occlusion of hydrogen gas in thehydrogen storage step (C) was almost sequentially continued. All ofthese operations were carried out at ambient temperature.

The results of analyzing the gas after purification in the hydrogenocclusion step (C), i.e., the gas (L5) occluded in the hydrogenocclusion alloy, using gas chromatography [GC-14A (trademark)manufactured by Shimadzu Corporation, carrier gas: argon] are as shownin the following Table 7, and the hydrogen concentration was increasedto 99.97 vol %, meanwhile the carbon dioxide concentration was decreasedto 0.03 vol %. In addition, the results of analyzing the hydrogenocclusion step off-gas (L6) containing carbon dioxide using gaschromatography [GC-14A (trademark) manufactured by Shimadzu Corporation,carrier gas: argon] are as shown in the following Table 8, and thecarbon dioxide concentration was 79.58 vol %, and hydrogen, carbonmonoxide and the like were detected in about 20.42 vol %.

TABLE 7 Component Concentration(vol %) Hydrogen 99.97 Carbon Dioxide0.03 Carbon Monoxide 0.00 Methane 0.00

TABLE 8 Component Concentration(vol %) Hydrogen 0.30 Carbon Dioxide79.58 Carbon Monoxide 0.00 Methane 20.12

Table 9 shows amount of the gas in each stream as the results ofrecovering hydrogen by treating 100 L of post-pyrolysis reformed gasobtained by heat-treating and reforming the pencil manufacture wastewood as described above. Herein, the unit of each number in Table 9 isliter. The second purified gas (L3) could be recovered in an amount of41.89 L based on 100 L of the fed reformed gas, and its recovery ratewas about 42 vol %. In addition, the reformed gas contained 61.42 L ofhydrogen, 38.51 L of which could be recovered. Furthermore, 38.50 L ofpurified hydrogen could be recovered by passing through the hydrogenocclusion step, and its recovery rate was approximately 63 vol %.

TABLE 9 First Second Hydrogen Hydrogen First Purification SecondPurification Occlusion Occlusion Reformed Purified Step Off- PurifiedStep Off- Step Purified Step Off- Component Gas Gas (L1) Gas (L2) Gas(L3) Gas (L4) Gas (L5) Gas (L6) Hydrogen 61.42 58.44 2.98 38.51 19.9338.50 0.01 Carbon Dioxide 23.02 5.07 17.95 2.70 2.37 0.01 2.69 CarbonMonoxide 8.89 0.00 8.89 0.00 0.00 0.00 0.00 Methane 6.67 1.35 5.32 0.680.67 0.00 0.68 Total 100.00 64.86 35.14 41.89 22.97 38.51 3.38

In the above-mentioned Example 1, the gas occluded in the hydrogenocclusion alloy charged in the adsorption columns in the hydrogenocclusion step, i.e., the first, second, third and fourth adsorptioncolumns (101, 102, 103, 104) was continuously taken out at that place.This embodiment is effective in a case where an apparatus for carryingout the method of the present invention is installed in the vicinity ofa facility utilizing high-purity hydrogen. In other embodiments, theadsorption columns in the hydrogen occlusion step is interchangeable sothat, after the hydrogen occlusion alloy in the first, second, third andfourth adsorption columns (101, 102, 103, 104) has stored hydrogen, theycan be replaced with new adsorption columns in which hydrogen is notstored yet so as to continue operation. The adsorption columns in whichthe hydrogen occlusion alloy has stored hydrogen can be moved as it isto the vicinity of a facility utilizing high-purity hydrogen for use. Inaddition, the adsorption column itself is designed to have the sameshape or the like as that of a hydrogen storage container in aninstrument equipped with a fuel cell so that the adsorption column inwhich hydrogen is stored can be used as it is as a hydrogen storagecontainer in an instrument equipped with a fuel cell utilizing hydrogenas fuel.

INDUSTRIAL APPLICABILITY

Since a high concentration of hydrogen gas can be recovered by using arelatively low pressure in the hydrogen recovery method of the presentinvention, the operation and apparatus costs can be considerablyreduced, furthermore the safety in operation can be remarkably enhanced.In addition, recovery and storage of hydrogen as well as utilization ofhydrogen can be achieved very efficiently because recovered high-purityhydrogen can be stored in a predetermined container, particularly acartridge-type container which can be used as it is as a hydrogenstorage container in an instrument equipped with a fuel cell utilizinghydrogen as fuel. Therefore the method is expected to be greatlyutilized for hydrogen recovery from a pyrolysis gas obtained byheat-treating biomass in the future.

REFERENCE NUMERALS

-   I First Purification Step-   II Second Purification Step-   III Biomass Heat-Treating Step-   IV Hydrogen Storage Step-   a Biomass-   b Pyrolysis Gas-   c First Purified Gas-   d Second Purified Gas (Gas Mainly Containing Hydrogen)-   e Gas Mainly Containing Carbon Dioxide-   f Gas Containing Carbon Dioxide-   g Hydrogen Occlusion Step Off-Gas-   h Gas Occluded in Hydrogen Occlusion Alloy (High-Purity Hydrogen)-   A First Purification Step-   B Second Purification Step-   C Hydrogen Storage Step-   L1 First Purified Gas-   L2 First Purification Step Off-Gas Mainly Containing Carbon Dioxide-   L3 Second Purified Gas-   L4 Second Purification Step Off-Gas Containing Carbon Dioxide-   L5 Gas Occluded in Hydrogen Occlusion Alloy (High-Purity Hydrogen)-   L6 Hydrogen Occlusion Step Off-Gas-   10 Compressor in First Purification Step-   11 First Adsorption column in First Purification Step-   12 Second Adsorption column in First Purification Step-   13 Third Adsorption column in First Purification Step-   14 Fourth Adsorption column in First Purification Step-   VI11 Inlet Valve of First Adsorption column-   VI12 Inlet Valve of Second Adsorption column-   VI13 Inlet Valve of Third Adsorption column-   VI14 Inlet Valve of Fourth Adsorption column-   VO11 Outlet Valve of First Adsorption column-   VO12 Outlet Valve of Second Adsorption column-   VO13 Outlet Valve of Third Adsorption column-   VO14 Outlet Valve of Fourth Adsorption column-   VM11 Adsorption Gas Withdrawal Valve of First Adsorption column-   VM12 Adsorption Gas Withdrawal Valve of Second Adsorption column-   VM13 Adsorption Gas Withdrawal Valve of Third Adsorption column-   VM14 Adsorption Gas Withdrawal Valve of Fourth Adsorption column-   Compressor in Second Purification Step-   First Adsorption column in Second Purification Step-   Second Adsorption column in Second Purification Step-   Third Adsorption column in Second Purification Step-   Fourth Adsorption column in Second Purification Step-   VI21 Inlet Valve of First Adsorption column-   VI22 Inlet Valve of Second Adsorption column-   VI23 Inlet Valve of Third Adsorption column-   VI24 Inlet Valve of Fourth Adsorption column-   VO21 Outlet Valve of First Adsorption column-   VO22 Outlet Valve of Second Adsorption column-   VO23 Outlet Valve of Third Adsorption column-   VO24 Outlet Valve of Fourth Adsorption column-   VM21 Adsorption Gas Withdrawal Valve of First Adsorption column-   VM22 Adsorption Gas Withdrawal Valve of Second Adsorption column-   VM23 Adsorption Gas Withdrawal Valve of Third Adsorption column-   VM24 Adsorption Gas Withdrawal Valve of Fourth Adsorption column-   31 Intermediate Tank-   32 Intermediate Tank-   30 Compressor in Hydrogen Occlusion Step-   101 First Adsorption Column in Hydrogen Occlusion Step-   102 Second Adsorption Column in Hydrogen Occlusion Step-   103 Third Adsorption Column in Hydrogen Occlusion Step-   104 Fourth Adsorption Column in Hydrogen Occlusion Step-   VI31 Inlet Valve of First Adsorption Column-   VI32 Inlet Valve of Second Adsorption Column-   VI33 Inlet Valve of Third Adsorption Column-   VI34 Inlet Valve of Fourth Adsorption Column-   VO31 Outlet Valve of First Adsorption Column-   VO32 Outlet Valve of Second Adsorption Column-   VO33 Outlet Valve of Third Adsorption Column-   VO34 Outlet Valve of Fourth Adsorption Column-   VM31 Occlusion Gas Withdrawal Valve of First Adsorption Column-   VM32 Occlusion Gas Withdrawal Valve of Second Adsorption Column-   VM33 Occlusion Gas Withdrawal Valve of Third Adsorption Column-   VM34 Occlusion Gas Withdrawal Valve of Fourth Adsorption Column

The invention claimed is:
 1. A method for recovering hydrogen frompyrolysis gas obtained by heat-treating biomass, comprising: a firstpurification step in which gas mainly containing carbon dioxide isadsorbed and removed from the pyrolysis gas under increased pressures topurify the pyrolysis gas; and a second purification step in which, at apressure not higher than that in the first purification step, thepurified gas obtained from the first purification step is furtherpurified by adsorbing and removing gas containing carbon dioxide fromthe purified gas under increased pressure to recover a gas mainlycontaining hydrogen from the purified gas, and the method furthercomprises a hydrogen storage step in which the gas mainly containinghydrogen recovered in the second purification step is supplied to acontainer filled with a hydrogen occlusion alloy so as to store highpurity hydrogen in the container, wherein the pressure in the firstpurification step is 0.15 MPa to 0.6 MPa, the pressure in the secondpurification step is 0.15 MPa to 0.6 MPa and a pressure in the hydrogenstorage step is 0.15 MPa to 0.6 MPa, wherein an adsorbent used foradsorbing and removing the gas mainly containing carbon dioxide in thefirst purification step is imogolite and/or amorphous aluminum silicate,and an adsorbent used for adsorbing and removing the gas containingcarbon dioxide in the second purification step is activated carbonand/or zeolite.
 2. The method for recovering hydrogen according to claim1, wherein the container filled with the hydrogen occlusion alloy is ofa cartridge type which can be used as it is as a hydrogen storagecontainer in an instrument equipped with a fuel cell utilizing hydrogenas fuel.
 3. The method for recovering hydrogen according to claim 2,wherein the instrument equipped with the fuel cell utilizing hydrogen asfuel is selected from a group consisting of: an automobile, a backuppower supply, a radio, a mobile phone, an unmanned airplane and adomestic thermoelectric supply system.
 4. The method for recoveringhydrogen according to claim 1, wherein a differential pressure betweenthe pressure in the first purification step and the pressure in thesecond purification step is 0 to 0.3 MPa.
 5. The method according toclaim 1, wherein the pyrolysis gas encompasses gas obtained bysteam-reforming the pyrolysis gas obtained by heat-treating the biomass.6. The method for recovering hydrogen according to claim 2, wherein adifferential pressure between the pressure in the first purificationstep and the pressure in the second purification step is 0 to 0.3 MPa.7. The method for recovering hydrogen according to claim 3, wherein adifferential pressure between the pressure in the first purificationstep and the pressure in the second purification step is 0 to 0.3 MPa.8. The method according to claim 2, wherein the pyrolysis gasencompasses gas obtained by steam-reforming the pyrolysis gas obtainedby heat-treating the biomass.
 9. The method according to claim 3,wherein the pyrolysis gas encompasses gas obtained by steam-reformingthe pyrolysis gas obtained by heat-treating the biomass.
 10. The methodaccording to claim 4, wherein the pyrolysis gas encompasses gas obtainedby steam-reforming the pyrolysis gas obtained by heat-treating thebiomass.
 11. The method for recovering hydrogen according to claim 1,wherein the adsorbent used for adsorbing and removing the gas mainlycontaining carbon dioxide in the first purification step is a singlelayer of imogolite or amorphous aluminum silicate, and an adsorbent usedfor adsorbing and removing the gas containing carbon dioxide in thesecond purification step is a single layer of activated carbon orzeolite.